Heretofore marine piers constructed for stability when standing on seabed in water deeper than 100 feet have proposed to store fluid materials in one centered tank or in a cluster of tanks having upright axes carried on a base slab and extending upwardly beyond the level reached by the largest amplitude gravity waves propagating over the site. Such piers have required the construction of a peripherally-complete surrounding wall capable of transforming the full energy of incident waves to solely kinetic energy of stream flow of seawater as jets guided by the bounding surfaces of channels constituted by perforations opening through the wall, as fully described in U.S. Pat. No. 3,383,869 to G. E. Jarlan.
The construction of the prior art pier requires an initial drydock building phase to fabricate a pan or raft upon which the bottom of the tank cluster is erected and which extends radially to provide a base for the surrounding perforated wall, followed by slip-forming of the upwardly-extending concrete structures, towing the pier structure to a site, and lowering it to stand on seabed, as described for example in Civil Engineering, August, 1973, Gerwick Jr., and Hogenstad, E. -- "Concrete Oil Storage Tank Placed on North Sea Floor".
Two disadvantages of the prior structure and method are evident in attempting to scale the dimensions of the prior pier upward to stand in very deep water and store a volume of fluid of the order of three million barrels, namely, the increased moment arm at which the lateral thrust due to wave forces is directed toward the structure, increasing the risk of sliding and unsafe rocking displacements, and, the greater cost per unit of storage volume due to the longer fabrication time required and the larger mass of concrete, reinforcement, and post-tensioned steel tendons necessary to build a perimetral perforated wall. A protected deep-water building site at which a pier of vertical extent approaching even 300 feet can be built is rarely available within a safe towing distance from the final site.
Even when the storage chambers of the prior art pier may be depressed so that their upper ends do not extend above the sea surface, to reduce wave pressures, the difficulties noted above would apply, compounded by any climatic obstacles such as frequent bad weather, distances from sources of construction materials and expense of maintaining a large working force by ship supply.